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nanotimes News in Brief

11-11/12 :: November/December 2011

Magnetism // New Magnetic-Field-Sensitive Alloy Could Find Use in Novel Micromechanical Devices

© Text: NIST L

ed by a group at the University of Maryland, a multi-institution team of researchers has com-

bined modern materials research and an age-old metallurgy technique to produce an alloy that could be the basis for a new class of sensors and microme- chanical devices controlled by magnetism. The alloy, a combination of cobalt and iron, is notable, among other things, for not using rare-earth elements to achieve its properties. Materials scientists at the National Institute of Standards and Technology (NIST) contributed precision measurements of the alloy‘s structure and mechanical properties to the project.

The alloy exhibits a phenomenon called “giant magnetostriction,” an amplified change in dimen- sions when placed in a sufficiently strong magnetic field. The effect is analogous to the more familiar piezoelectric effect that causes certain materials, like quartz, to compress under an electric field. They can be used in a variety of ways, including as sensitive magnetic field detectors and tiny actuators for micro- mechanical devices. The latter is particularly in- teresting to engineers because, unlike piezoelectrics, magnetostrictive elements require no wires and can be controlled by an external magnetic field source. To find the best mixture of metals and processing, the team used a combinatorial screening technique,

TEM (transmission electron microscope) image taken at NIST of an annealed cobalt iron alloy. The high magneto- striction seen in this alloy is due to the two-phase iron-rich (shaded blue) and cobalt-rich (shaded red) structure and the nanoscale segregation. © Bendersky/NIST

fabricating hundreds of tiny test cantilevers – tiny, 10-millimeter-long, silicon beams looking like diving boards – and coating them with a thin film of alloy, gradually varying the ratio of cobalt to iron across the array of cantilevers. They also used two different heat